The present invention relates, in general, to a hot runner system, and in particular to a hot runner nozzle for an injection molding machine or plastics injection mold.
A hot runner nozzle is, for example, known from European Pat. No. 0 137 888 A2 and includes a central heating rod which is surrounded by a sleeve which is radially split to form two sleeves. Arranged between the heating rod and the split sleeve is an electric insulation, with the heating rod having opposite free ends which are electrically connected to the adjacent ends of the sleeves, while the opposite adjoining ends of the sleeves are formed with a flange for introduction of electric current.
This type of conventional hot runner nozzle has the drawback that the split outer sleeves are formed with flanged enlargements which are separated by an electric insulation while the insulation extends to the flow channel traversing the flanges. Thus, the insulation comes into contact with the melt and hence is exposed to all forces and loads as generated by the construction and operational loads, such as erratically changing extremely high pressures of the flowing melt. This is especially disadvantageous when the melt contains solids such as fiberglass fractions.
Also, the beginning destruction of the insulating layers results in the creation of voids which are being filled by the melt, leading to dead spaces and complicating a paint change or material change, in the event such changes become necessary. Melt migrating into the gaps formed as a result of a destruction of the insulation acts on the thus-exposed surfaces of the flanges to push them apart so that melt can penetrate, ultimately destroying the functionality of the nozzle.